Habilidade competitiva de cultivares de cana-de-açúcar inoculadas com bactérias diazotróficas fixadoras de nitrogênio

Abstract

Sugarcane (Saccharum spp.) can establish association with diazotrophic bacteria, which promotes the growth of the crop through N fixation and the production of compounds, such as some phytormons. The aim with this study was to evaluate the competitive ability of sugarcane inoculated of diazotrophic nitrogen fixation in relation to weeds. Two experiments were carried out, one with cultivar RB92579 and one with RB867515. A completely randomized experimental design, with four replicates, was used. The treatments were composed of a 2 x 4 factorial. The first factor was related to the inoculation, or not, of sugarcane buds with a mixture of strains of some bacteria (Herbaspirillum rubrisubalbicans, Herbaspirillum seropedicae, Azospirillumam azonense, Gluconacetobacter diazotrophicus and Burkholderia tropica), and the second factor was related to the coexistence of the crop with weeds (Digitaria horizontalis, Amaranthus retroflexus, Bidens pilosa and free of infestation). The strains of the bacteria were inoculated in the micro-cuts of the cultivars, according to the treatments, followed by their planting in pots of 12 dm3 filled with amended soil (Red Latosol). The weeds were transplanted (5 plants per pot) at the time of sugarcane emergence. At 35, 50, 65 and 80 days after sugarcane emergence the plant size, number of leaves, number of tillers, stem diameter, leaf area, leaf chlorophyll content and leaf nitrogen content were assessed. In the last day of assessment, the shoot mass, root system volume, root system length and dry mass of the root system were assessed for the sugarcane and weed plants. The inoculation with nitrogen-fixing bacteria did not present significant contributions in the development of the crop, contributing only to the growth in height. Weed species negatively affected the development of sugarcane, interfering in the accumulation of root- and shoot-dry matter mass and also in the volume of roots. Digitaria horizontalis was the species that caused the greater negative effect. The inoculation of diazotrophic nitrogen-fixing bacteria does not contribute to the competitive ability of sugarcane.